Kepler-37b: Smallest planet yet found beyond our solar system discovered by NASA

(CNN) -- It's not the kind of place you'd call home: an airless, rocky planet so close to its sun that some metals will melt on its surface.

But it's a big little discovery for NASA's space observatory Kepler. The space agency says the planet, dubbed Kepler-37b, is the smallest yet found beyond our solar system.

Slightly larger than the moon and about a third the size of Earth, it's one of three planets circling the star Kepler-37, NASA announced Wednesday -- and the first of dozens of discovered exoplanets known to be smaller than any that orbit our sun.

The findings were reported in this week's edition of the journal Nature.

Kepler-37 is located 210 light-years away in the constellation Lyra, and it's slightly smaller and cooler than our sun. Kepler 37-b circles it closely, completing its "year" every 13 Earth days, the NASA-led team of scientists wrote.

All three planets found in the system are in orbits closer than Mercury. NASA estimates Kepler-37b's surface temperature at about 800 degrees F (427 C), hot enough to melt metals like lead, zinc or tin.

The $600 million Kepler mission was launched in 2009 and has been scanning a patch of about 150,000 stars in our end of the galaxy for planets orbiting in habitable zones. It has found more than 100 other confirmed planets, ranging from about 1.5 times the size of Earth to larger than Jupiter.